The invention concerns an automatic clutch in the drive train of a motor vehicle, which has between the engine and the drive wheels a transmission which can be shifted manually and arbitrarily between different gears or drive positions with different transmission ratios. A motorized adjusting unit actuates the clutch. A system of sensors, which serves for controlling the adjusting unit, senses a parameter correlated with the speed of a gear change or change of drive position and the signals of which initiate or control, among other things, a releasing and engaging of the clutch when the gears or transmission stages are changed.
In motor vehicles having customary internal combustion engines, a transmission is arranged in the drive train. The transmission allows the transmission ratio between the speed of the vehicle engine and the speed of the drive wheels to be changed according to the respective travelling speed and loading of the vehicle. In the case of customary manually shifted transmissions, during a change of drive position the power flow between the engine and the drive wheels has to be interrupted by releasing a clutch.
It is known in principle to use automatic clutches for this purpose, i.e. the clutch is automatically released when changing the transmission stage and is subsequently re-engaged.
It is known in this connection from German Patent document DE 195 48 799 A1 to sense a parameter controlled by the speed of a gear change in order to release the clutch particularly quickly when a shift lever or the like (actuated for the gear change) is actuated at high speed.
In addition, the clutch is also automatically controlled when starting the vehicle. As soon as a drive position suitable for starting has been selected, the clutch can, for example, be automatically engaged lightly in such a way that a small torque adequate for making the vehicle begin to slowly creep forward is transmitted. As soon as the engine power and the engine speed are increased by actuating a gas pedal or some other power control element, the clutch is automatically controlled in the sense of increasing the transmissible torque. To put it in simple terms, the clutch is then increasingly engaged.
The engaging operation of the clutch after changing gears or drive positions can, in principle, be controlled in various ways. In this connection, it has proved to be advantageous to take into account a difference in speed between the clutch input and the clutch output during the engaging phase. For this purpose, on the one hand the engine speed (determining the speed of the clutch input), and on the other hand the speeds of the drive wheels are sensed, for example. In connection with the respectively selected gear or the respectively selected transmission stage, these wheel speeds determine the speed of the output of the clutch arranged between the engine and the transmission. The signals for the engine speed are readily available because modern vehicle engines are regularly equipped with electronic controls, which have to sense the speeds of the engine to control it. The wheel speeds are regularly inquired for controlling a brake system with an anti-lock system. Consequently, for controlling the clutch it merely has to be ensured that signals for the above-mentioned parameters are also sent to the clutch control. As a result, it is consequently possible to achieve very smooth clutch engagement and, in particular, an engagement of the clutch which is free to the greatest extent from any jerking movements.
The object of the invention is thus to improve clutch control still further.
This object is achieved according to the invention by an adjusting unit which controls the engaging operation of the clutch while a gear change or change of drive position is taking place as a function of the parameter correlated with the speed of the gear change or change of drive position. This is done in such a way that a phase in which clutch slippage occurs, provided during clutch engagement, is shortened increasingly with increasing shifting speed.
The invention is based on the general idea of taking into account during clutch control whether the driver is performing a gear change or change of transmission stage quickly or slowly. Consequently, a parameter which reproduces whether the driver would like to drive in a more sporty style or with more emphasis on comfort is sensed. Depending on the shifting behavior of the driver, the engaging operation of the clutch can then be quickly controlled with more emphasis on comfort or in a more sporty manner.
A particular advantage of the invention is that, for sensing the shifting speed, only the signals of sensors which are already present in the vehicle for other reasons have to be evaluated. For instance, the transmission is regularly assigned a sensor arrangement which senses the selected gear or the selected drive position. The signals of this sensor arrangement can accordingly detect whether and when a previously selected gear or a previously selected transmission stage is left and when a gear or a transmission stage is to be selected once again. The time difference occurring between these signals is a parameter for the shifting speed.
In addition, the shifting element of the transmission may be assigned a potentiometer or the like, which senses movements of the shifting element and serves, among other things, for detecting shifting intended by the driver. The shifting speed can also be derived from the signals of the potentiometer.
According to a particularly preferred embodiment of the invention, when controlling the engaging operation of the clutch, the position of a gas pedal actuated by the driver or some other element for driver control of the driving performance is taken into account. Consequently, there is, for example, the possibility of engaging the clutch quickly after a gear change or change of drive position with a high shifting speed only if the driver wishes to make greater use of the potential power of the engine, in other words if the driver not only wishes to "shift in a sporty style" but also "drive or accelerate in a sporty style".
Otherwise, with regard to preferred features of the invention, reference is made to the claims and the following explanation of the drawing, on the basis of which a particularly advantageous embodiment is described.